The work will investigate whether anatomical and/or physiological changes in the auditory system of the deafened infant can be diminished or prevented by chronic electrical stimulation. Further, it will establish whether stimulation in the immediate post-natal period exerts a more salutary effect on development than if that stimulation is delayed. The studies will use deafened infant primates subject to chronic cochlear stimulation imposed immediately or delayed six months after deafness occurs. Periodic monitoring of the EABR will be used to assess the functional stability of the system. Comparison of anatomical development of cochlear nucleus size, individual spiral ganglion and cochlear nucleus cells, and 8th nerve fibers will be made among animals receiving stimulation on different delay schedules. It is hypothesized that animals undergoing early electrical stimulation will exhibit sustained physiological responses and normal growth of cells, whereas absence of early stimulation will result in lasting deficits in these measures. This research will generate significant insights related to theoretical issues concerning critical periods in development of hearing, which will be directly applicable to clinical management of early deafness in humans.